splice: add helpers for locking pipe inode

There are lots of sequences like this, especially in splice code:

	if (pipe->inode)
		mutex_lock(&pipe->inode->i_mutex);
	/* do something */
	if (pipe->inode)
		mutex_unlock(&pipe->inode->i_mutex);

so introduce helpers which do the conditional locking and unlocking.
Also replace the inode_double_lock() call with a pipe_double_lock()
helper to avoid spreading the use of this functionality beyond the
pipe code.

This patch is just a cleanup, and should cause no behavioral changes.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

1 files changed, 38 insertions, 4 deletions

diff --git a/fs/pipe.c b/fs/pipe.c
index 4af7aa521813..13414ec45b8d 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -37,6 +37,42 @@
  * -- Manfred Spraul <manfred@colorfullife.com> 2002-05-09
  */
 
+static void pipe_lock_nested(struct pipe_inode_info *pipe, int subclass)
+{
+        if (pipe->inode)
+                mutex_lock_nested(&pipe->inode->i_mutex, subclass);
+}
+
+void pipe_lock(struct pipe_inode_info *pipe)
+{
+        /*
+         * pipe_lock() nests non-pipe inode locks (for writing to a file)
+         */
+        pipe_lock_nested(pipe, I_MUTEX_PARENT);
+}
+EXPORT_SYMBOL(pipe_lock);
+
+void pipe_unlock(struct pipe_inode_info *pipe)
+{
+        if (pipe->inode)
+                mutex_unlock(&pipe->inode->i_mutex);
+}
+EXPORT_SYMBOL(pipe_unlock);
+
+void pipe_double_lock(struct pipe_inode_info *pipe1,
+                      struct pipe_inode_info *pipe2)
+{
+        BUG_ON(pipe1 == pipe2);
+
+        if (pipe1 < pipe2) {
+                pipe_lock_nested(pipe1, I_MUTEX_PARENT);
+                pipe_lock_nested(pipe2, I_MUTEX_CHILD);
+        } else {
+                pipe_lock_nested(pipe2, I_MUTEX_CHILD);
+                pipe_lock_nested(pipe1, I_MUTEX_PARENT);
+        }
+}
+
 /* Drop the inode semaphore and wait for a pipe event, atomically */
 void pipe_wait(struct pipe_inode_info *pipe)
 {
@@ -47,12 +83,10 @@ void pipe_wait(struct pipe_inode_info *pipe)
          * is considered a noninteractive wait:
          */
         prepare_to_wait(&pipe->wait, &wait, TASK_INTERRUPTIBLE);
-        if (pipe->inode)
-                mutex_unlock(&pipe->inode->i_mutex);
+        pipe_unlock(pipe);
         schedule();
         finish_wait(&pipe->wait, &wait);
-        if (pipe->inode)
-                mutex_lock(&pipe->inode->i_mutex);
+        pipe_lock(pipe);
 }
 
 static int